Examining the Symbioses between Millepora and Symbiodinium at Two Thermally Different Locations

Rising seawater temperatures have increased rates of coral mortality due to bleaching. Bleaching is a result of the loss of Symbiodinium, a photosynthetic protist, from coral tissues. Both temperature and light play important roles in the diversity of coral symbionts, and different Symbiodinium clades (A-I) provide different physiological benefits to their coral hosts. This symbiosis may provide coral with a mechanism to cope with thermal stress events associated with global warming.

The vast majority of the research examining the coral-Symbiodinium relationship has focused on Scleractinian (stony) corals, while ignoring the major reef-framework-building hydrozoan Millepores (fire coral). We are examining the diversity of the Millepore-Symbiodinium symbiosis at two thermally different Caribbean reef locations: San Salvador, Bahamas and South Water Cay, Belize. Our preliminary results indicate that sea surface temperature may play an important role in diversity of symbionts residing in Millepores. Clade B was the sole dominant symbiont found in coral colonies (N=28) collected in the Bahamas (northern Caribbean), where sea surface temperatures are cooler. Clade A was the dominant symbiont found in coral colonies (N=20) collected in Belize (southern Caribbean), where sea surface temperatures are slightly warmer. The difference in the dominant symbiont clades present appears to be associated with different environmental conditions at each geographic location and may reflect that the South Water Cay, Belize location is exposed to more frequent thermal stress events.